Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the semiconductor industry for IC fabrication and the like, and are attracting considerable attention.
These fine patterns are typically formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. For example, in the case of a lithography method, a process is conducted in which a resist film formed from a resist composition containing a base component such as a resin is formed on top of a support such as a substrate, the resist film is subjected to selective exposure using radiation such as light or an electron beam, through a mask in which a predetermined pattern has been formed (a mask pattern), and a developing treatment is then conducted, thereby forming a resist pattern of predetermined shape in the resist film. Resist compositions in which the exposed portions change to become soluble in the developing solution are termed positive compositions, whereas resist compositions in which the exposed portions change to become insoluble in the developing solution are termed negative compositions.
Then, using this resist pattern as a mask, a semiconductor device or the like is produced by conducting a step in which the substrate is processed by etching.
In recent years, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays semiconductor device mass production using KrF excimer lasers and ArF excimer lasers has already commenced, and for example, lithography using ArF excimer lasers has enabled pattern formation with resolution at the 45 nm level. Furthermore, in order to further improve the resolution, research is also being conducted into lithography techniques that use exposure light sources having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beams, EUV (extreme ultraviolet radiation), and X rays.
The resist composition requires lithography properties such as a high level of sensitivity to these types of exposure sources, and a high resolution capable of reproducing patterns of minute dimensions. As a resist material which satisfies these requirements, a chemically amplified resist composition is used, which includes a base component that exhibits changed alkali solubility under the action of acid and an acid generator that generates acid upon exposure (for example, see Patent Document 1). For example, a positive chemically amplified resist typically contains, as a base component, a resin which exhibits increased alkali solubility under the action of acid, and during formation of a resist pattern, when acid is generated from the acid generator upon exposure, the exposed portions of the resist become alkali-soluble.
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of the exposure apparatus and the sample is filled with a solvent (an immersion medium) that has a larger refractive index than the refractive index of air (see, for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that higher resolutions equivalent to those obtained using a shorter wavelength light source or a larger NA (numerical aperture) lens can be achieved using the same exposure light source wavelength, with no lowering of the depth of focus. Furthermore, immersion exposure can be conducted using a conventional exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as phase shift methods and modified illumination methods. Currently, as the immersion exposure technique, techniques using an ArF excimer laser as an exposure source are being the most actively studied. Further, water is mainly being investigated as the immersion medium.
Recently, a new lithography technique called the double patterning method has been proposed, in which a pattern is formed by conducting patterning two or more times (see, for example, Non-Patent Documents 2 and 3). It is considered that by using this double patterning method, a pattern can be formed that is finer than a pattern formed using only a single patterning step. For example, in Non-Patent Document 2, a method such as that shown in FIG. 2A through FIG. 2F is disclosed.
In other words, first, as shown in FIG. 2A, a laminate is prepared by laminating a substrate 101, a lower layer film 102, and a hard mask 103.
Next, a resist film is provided on top of the hard mask 103, and as shown in FIG. 2B, by selectively irradiating the resist film through a mask 105 and then performing developing, a resist pattern 104 is formed in which a plurality of trench patterns having a space width of d/4 are arranged at a pitch of d.
Subsequently, the hard mask 103 is etched using the resist pattern 104 as a mask, and the residual resist pattern 104 is then removed. As shown in FIG. 2C, this yields a hard mask 103′ to which the resist pattern has been transferred.
Next, as shown in FIG. 2D, the position of the mask 105 is shifted, and a resist material is coated onto the hard mask 103′, thereby filling the spaces within the hard mask 103′, and forming a thick-film resist film having a thickness greater than the thickness of the hard mask 103′. This resist film is selectively exposed through the shifted mask 105 and then developed, thereby forming a resist pattern 106.
Subsequently, the hard mask 103′ is etched using the resist pattern 106 as a mask, and the residual resist pattern 106 is then removed. As shown in FIG. 2E, this yields a hard mask 103″ having a transferred pattern in which a plurality of trench patterns having a space width of d/4 are arranged at a pitch of d/2.
Then, by conducting etching with the hard mask 103″ as a mask, the pattern of the hard mask 103″ is transferred to the lower layer film 102, enabling the formation of a pattern 102′ shown in FIG. 2F in which the pitch is ½ of that of the mask 105 that was used.
In this manner, according to the double patterning method, a resist pattern of higher resolution can be formed, even if a light source having the same exposure wavelength is used, and even if the same resist composition is used. Further, the double patterning method can also be used with existing exposure apparatus.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2003-241385
[Non-Patent Document 1]
Optronics 2003, No. 4, pp. 117 to 121 (2003)
[Non-Patent Document 2]
Proceedings of SPIE, vol. 5256, pp. 985 to 994 (2003)
[Non-Patent Document 3]
Proceedings of SPIE, vol. 6153, pp. 615301-1 to 615301-19 (2006)